This invention relates to a process for the production of pimelic acid and more particularly to a process for the production of pimelic acid from .epsilon.-caprolactone.
Pimelic acid (heptanedioic acid) and derivatives thereof are useful chemical compounds. For example, pimelic acid may be employed in the synthesis and manufacture of plasticizer esters, polyamides, alkyl resins, polyesters, polyurethanes, elastomers and a wide variety of other useful products, such as stabilizers, curing agents, lubricants and greases, fuel additives, adhesives and binders, paints, varnishes, corrosion inhibitors, soaps, detergents, bleaches and textiles.
More particularly and for example, pimelic acid copolymerizes with 1,5-pentanediamine to form Nylon 5,7. Recent research indicates that this odd Nylon (having an odd number of carbon atoms in each monomer unit) can be electrically active and may have potential as a conducting polymer. For example, see G. Froyer et al. J. Polymer Science, Polymer Chem. Ed., 19, 165-174 (1981).
Present electronic devices and electrically active materials are comprised of metals, semimetals, ceramics and other inorganic substances. In many applications, their utility is restricted by excess weight, mechanical fragility, fabrication problems, corrosion, scarcity and high cost. Thus, there has been a considerable interest in replacing these metals and inorganics with conducting polymers such as the afore-said Nylon.
Use of pimelic acid, however, in meeting this need to provide conducting polymers, for example, is limited by the high cost of its production. Known syntheses for pimelic acid include the non-selective oxidation of expensive starting materials, such as cycloheptanone, 1,7-heptanediol, 1,5-dicyanopentane or ricinoleic acid. U.S. Patents which disclose some syntheses for pimelic acid include U.S. Pat. No. 2,800,507, U.S. Pat. No. 2,826,609, U.S. Pat. No. 3,600,420, U.S. Pat. No. 2,698,339, U.S. Pat. No. 2,826,609 and U.S. Pat. No. 2,800,507.
A particularly interesting synthesis for the preparation o dicarboxylic acids and particularly pimelic acid, is disclosed in Japanese Patent No. 79-92913. This synthesis involves reacting lactones with carbon monoxide in the presence of a platinum group compound, such as a rhodium compound, as a catalyst, and an iodine compound, such as methyl iodide, as a promoter. Moreover, this Japanese patent discloses other prior art syntheses of dicarboxylic acids which involve the carbonylation of lactones including .gamma.-valerolactone, .gamma.-butyrolactone, or -.delta.-valerolactone in the presence of an iodine compound and a nickel or cobalt compound under high pressures and temperatures.
U.S. patents which disclose the preparation of dicarboxylic acids from lactones include U.S. Pat. No. 2,449,987, U.S. Pat. N. 2,444,988, U.S. Pat. No. 3,849,457 and U.S. Pat. No. 3,342,838.
The use of .epsilon.-caprolactone as a starting material in the preparation of pimelic acid offers a selective and potentially economic route for its preparation. However, improved synthetic methods which provide pimelic acid more selectively and in higher yields are desired if the applications of this dibasic acid are to be expanded as indicated hereinabove.